1. Field of the Invention
This invention relates to a semiconductor light emitting device of a novel structure wherein the modulation of a semiconductor laser element is effected with transistors which are integrated and disposed on the same substrate as that of the semiconductor laser.
2. Description of the Prior Art
A semiconductor laser element provides a wide application in, for example, optical communication systems such as data bus or computer-link since it is small in size and capable of performing rapid modulation.
The modulation of a semiconductor laser element is usually performed in such a manner as described below. A direct current is sent through a circuit element called a bias-T unit, consisting of a capacitor and a coil, from the side of the coil; the excitation concentration is raised up to near the laser oscillation threshold; and the laser output light is modulated through the superposition of a current pulse of 30 to 70 mA sent from the side of the capacitor. Such apparatus have been put on the market. However, in the case where a high speed modulation of 1 to 2 Gbits/sec. is desired according to the above method, it is difficult for ordinary silicon transistors to generate such current pulses as suitable for the high speed modulation. Moreover, the bias-T unit is very voluminous in comparison with the laser element and the size of a laser apparatus incorporating therein many laser elements cannot be made compact.